1. Field of the Invention
The present invention relates to power subsystem architectures, and more particularly, to a power subsystem that actively provides energy management and control of subsystem efficiency by using power-loss models of power devices.
2. Description of Related Art
It is well known in the art to use a distributed power subsystem architecture comprising multiple power conversion stages to provide necessary bus voltages for microprocessors, memories, and other electronic devices. A conventional system might operate from an alternating current (AC) primary voltage source that is converted to an intermediate direct current (DC) bus voltage using an isolated AC/DC converter. This intermediate DC bus voltage is then typically distributed throughout the system and converted locally by secondary DC/DC converters to lower voltages matched to the input voltage requirements of system loads. Alternatively, a system might operate from a primary DC bus voltage that is first converted to an intermediate bus voltage by an isolated DC/DC converter. The intermediate voltage is again distributed to secondary regulators or converters to provide the required supply voltages. Examples of conventional systems are depicted in FIGS. 1 and 2 which illustrate, respectively, an AC system operating at 230 VAC with an intermediate bus at 12 VDC, and a DC system operating at 48 VDC with an intermediate bus at 12 VDC.
The efficiency of any power converter or regulator is typically a complex function of its operating point, depending on the input voltage, the output voltage, the load current, and the temperature of the device, among other parameters. Thus, the efficiency will typically vary with system activity as loads are switched on or off or run at high or low clock rates and as the system heats up or cools down. Nevertheless, once designed and optimized for a particular operating point, conventional power subsystems are operated statically, regardless of system activity.
In the system depicted in FIG. 1, the efficiency of the primary power converter will tend to increase as the input voltage increases, and the efficiency will decrease as the output voltage decreases and as the temperature rises. Similarly, the efficiency of the regulators will tend to increase as the input voltage decreases and as the output voltage rises, and the efficiency will decrease as the temperature rises. The behavior of the system in FIG. 2 is similar. Thus, it is clear that the selection of the intermediate voltage will affect the efficiency of the overall system. Lowering the intermediate voltage will reduce the efficiency of the primary converter but raise the efficiency of the secondary regulators. Thus for a given operating state of the system, there is an optimal intermediate voltage that will maximize the overall efficiency of the system. Similarly, although the efficiency of both the primary converter and the secondary regulators decrease as the temperature increases, operating a fan or other active cooling system consumes power and thus reduces system efficiency. Thus, there is also an optimal temperature set point for a given operating state of the system that will maximize power efficiency.
In a typical system, the power subsystem is optimized for a single operating point that would preferably be the operating point at which the system would be found most often. The intermediate voltage and temperature control point are set to this operating point and generally remain fixed, regardless of the actual operating state of the system. However, to reduce total energy consumption, it would be better to dynamically optimize the set points of the power subsystem based on actual system activity. However, in many cases, it is impractical to measure the power loss of a power conversion device directly with enough accuracy to enable effective control. For the most part, this is because measuring the power loss involves taking the difference of two large quantities, the input power and the output power, to arrive at a small power loss measurement. For example, a typical converter might run at an input power of 100 W and an output power of 92 W, resulting in a power loss of 8 W. If the input and output power losses can each be measured with a precision of ±2%, which is a challenge in itself, the calculation of the power loss will exhibit a large combined error as illustrated below:(100 W±2 W)−(92 W±1.8 W)=8 W±2.7 W,assuming that the input and output power measurement errors are uncorrelated. In other words, the error of the power loss measurement is +/−34%, which is clearly far too imprecise to use for effective control of system efficiency. As the efficiency of power converters improves as the technology advances, this problem only gets worse as the power losses become increasingly smaller compared to the input and output powers.
Thus, it would be useful to provide a power subsystem that utilizes active control to dynamically optimize design set points in order to maximize subsystem efficiency as system activity changes. And it would be useful to provide a method of characterizing and monitoring the power loss of the power subsystem components in a manner that provides sufficient precision to enable the dynamic optimization of design set points.